Electrical network



April 21, 1931- D. K. GANNETT ET AL 1,801,342

ELECTRI CAL NETWORK Original Filed April 27, 1920 IN V EN TORS (j A TTORNEY Patented Apr. 21, 1931 UNITED STATES PATENT OFFICE DAN FORTH K. GANNET'I', OF JACKSON HEIGHTS, NEW YORK, AN D MACLEAN KIRKWOOD, OF TOWACO, NEW JERSEY, ASSIGNORS TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A. CORPORATION OF NEW YORK ELECTRICAL NETXVORK Original application filed April 27, 1920, Serial No. 376,996. Patent No. 1,638,437, dated August 9, 1927. Divided and this application filed. July 2, 1927. Serial No. 203,080.

This invention relates to electrical networks, and especially to a type of aperiodic network which is adapted to modify the voltage wave impressed thereon in such manner that the wave at the output end of the said network closely approximates in form any desired integral or derivative of the impressed wave depending upon the type of network used.

, This application is a division of the copending application, Serial No. 376,996, filed April 27, 1920, which issued on August 9, 1927, as Patent No. 1,638,437, and is intended to cover and to claim specifically that form of network by which any desired derivative of the impressed wave may be obtained.

Networks heretofore devised for approximating a required integral or derivative of an impressed voltage wave may be rendered free from undesirable interaction between the component parts only by the insertion of some form of unilateral device at suitable points, or by proportioning the constants of the successive networks so that the current transmitted therethrough becomes unduly diminished, or by greatly increasing the im-- pedance of the circuits. 7

It is the object of the present invention to provide networks involving resistances, i11- ductances and capacities combined so that the output voltage wave of such networks when combined will closely approximate any required integral or derivative of the wave impressed upon said combined networks, which networks require no unilateral devices to prevent interaction between the parts and do not cause undue diminution of the transmitted current, or other undesirable results.

The integrating or differentiating networks of this invention are of the nature of low pass and high pass filters respectively.

The integrating networks simulate the low pass type, being designed to transmit with slight attenuation a range of low frequencies and to attenuate greatly the frequencies above a certain critical frequency. In a converse manner, the differentiating networks transmit readily the upper range or band of frequencies and subject the lower frequencies to greater attenuation. It will be shown later that the integrating networks produce a wave that closely approximates a true integral of the impressed wave throughout the frequency range above the aforesaid critical frequency, and similarly the differentiating network approximates a true derivative of the impressed wavethrough the frequency range below the critical frequency, the said critical frequency depending on the time-constant of the circuit.

Such networks, especially of the integrating type, are found advantageous in submarine cable telegraphy, in order to screen the receiving apparatus of such cables from the efiects of transient interference waves set up in said cable, and at the same time to freely transmit the signaling waves received over the said cable. This invention has accordingly been described in its relation to such type of telegraphy, but it is to be understood, however, that it is not so limited, but may be used in any type of circuit where it is desired to obtain any integral or derivative of a variable voltage wave.

This invention will be better understood from the following description when read in connection with the attached drawing, of which Figure 1 shows the arrangement of the network for four successive integrations of an impressed voltage wave; Fig. 1a is a modification of the amplifier connection shown in Fig. 1; Fig. 2 shows in detail one unit illus' trating the basic principles involved; Fig. 2a

In Fig. 1, 1 represents a transmission line having large distortion and attenuatlon characteristics such as a submarine telegraph cable, which is connected to a winding 12 of the transformer 5, the other side of said winding being connected to an artificial line 2, adapted to balance the submarine cable. A transmitting device 3 which may be of any well known type is connected to the midpoint of winding 12. Bridged across the other winding 4. of the transformers 5 is an inter ference reduction network comprising four sub-networks 6, 7, 8 and 9, each of the said sub-networks comprising an inductance L in series with the line, a resistance R and a capacity C in series with the said resistance bridged across the line. Network 9 terminates in resistance R the value of which may be determined by equations hereinafter set forth. Across R is bridged the input side of a vacuum tube amplifier 10, which is adapted to impress theamplified wave upon a recording device 11. The same result would be obtained by bridging the input side of the amplifier across the condenser C in the manner shown in Fig. 1a.

Fig. 2, as stated, shows a single unit embodying the basic principles of this invention, comprising two parallel circuits, one of which has in series a resistance R and a capacity C and the other of which has in series a resistance R equal to the resistance R, and

in series therewith an inductance L It will be shown later that the impedance of such circuit when its constants are properly proportioned is equal to the. resistance in either branch at all frequencies. Accordingly, there may be substituted for the resistance R, another network similar to that shown in Fig. 2, which arrangement is illustrated clearly in Fig. 2a.

Fig. 3 shows means for combining a plurality of sub-networks as shown in Fig. 2

so as to obtain, for example, at the output side of the said network the fourth integral of the impressed voltage wave.

It will be seen that the network shown in Fi 1 in con .nection with the terminal circuit of a submarine cable telegraph system is only a rearrangement of t 1e circuit shown in Fig. 3. Fig. 4; shows graphically the relationbetween the ratio of the output voltage to the input voltage of the network and the frequency when a network such as is shown in Figs. 1 and 3 is inserted in the circuit. The curves at, b, and '0 represent respectively the first, third and fourth integralsof theimpre-ssed voltage wave. It will be noted that the curves fall off sharply after passing a certain frequency value. Since the interference waves are of relatively high frequency compared with the signaling waves, they will be reduced in magnitude whereas thesignaling frequency will pass through the network substantially unalfected thereby.

Fig. 5 shows the arrangement of the network to obtain for example, the fourth derivative of an impressed voltage wave. It comprises four sub-networks, each of which is made up of a capacity C in series with the line and a resistance R in series with an inductance L, connected across the line. Bridged across the last network is a resistance R the value of which may be determined by equations here inafter'set forth. The network of 5 1nay be derived by extending the fundamental network shown in 2 by a process of substitution, in general, similar to the method of developing the integrating networks shown in Figs. 2, 2a and 3, but differing therefrom in that each additionalnetwork replaces the resistance in the capacity branch instead of the resistance in the inductance branch of the preceding network. Each of these sub-networks produces a voltagewave which is the derivative of the wave impressed thereon. It will be seen, therefore, that any desired derivative may be obtained by connecting together in the manner shown, a number of sub-networks corresponding to the desired derivative. The same result may be obtained by an inductive coupling shown in Fig. 5a across the inductance L, since the voltage wave across L is the same as that across the resistance R Having in mind the foregoing description of the circuits and the functions of'the component parts, this invention will be more clearly understood from the following description of the manner in which the circuit operates when an impressed variable voltage wave, such as a signal wave is impressed across the winding 4 of the transformer 5.

Consider first the unit network shown in Fig. 2. If the two resistances therein represented by R and R are each equal to E J and the lnductance L is assumed to have Zero resistance, the network as shown in the figure will have an impedance equal to the resistance 11 3 for all frequencies of the impressed wave. This will be seen from the following derivation of the impedance of the circuit:

or O=g the above equation by substitution becomes Since, therefore, the impedance of the circuit represented in Fig. 2 is equivalent to R,

we may substitute such a circuit for the resistance R in the manner shown in Fig. 2a. In this figure, the elements R 0 and L are the same as the similarly designated parts of Fig. 2, but in place of the resistance R we have substituted a circuit of equivalent impedance comprising a resistance R a capacity C an inductance L and a resistance R". This process may be carried further by substituting for R a third network, and by thus adding to the basic network the required number of sub-networks, we may provide a structure adapted to produce approximately the required integral of the impressed voltage wave.

Further consideration of the unit network shown in Fig. 2 in'connection with the fol lowing description, will make clear the reason why the output voltage across the network closely approximates an integral of the impressed voltage wave.

Assuming a voltage E impressed across the network, the voltage drop 6 across the resistance R in terms of the impressed voltage is R" ri 17m (1) If the frequency is above a certain critical value the voltage drop across the inductance L is substantially E, and consequently the current through L is related to the voltage E substantially in accordance with the following equation:

which, when rearranged in form, is

1 E 1 ead-El If we multiply the preceding equation by R, we obtain It will be seen that Equation 1 approaches in value Equation 2 for these frequencies at which the voltage drop across the inductance L is substantially equal to E, because at those frequencies jwL becomes large relative to R. Therefore, the network as shown in Fig. 2 may be said to approximately integrate the impressed voltage wave for frequencies above the critical frequency, and the approximation to an exact integral being proportional to the distance from the critical frequency.

In a similar manner, it may be shown that forfrequencies below a limiting value, such that the impedance of the condenser C is great compared with its resistance R the current through the condenser and hence the voltage across the resistance approximates the first derivative of the voltage E. The limiting value of frequency below which this approximationapproaches the actual condition is proportional to the reciprocal of the time constant of C and R and therefore may be made any required value.

Since, however, it is impracticable to obtain inductance coils having zero resistance, the values of the elements of the networks must be modified in order to apply this principle to a practical case. If R represents the resistance of one inductance coil, the conditions which must be satisfied are that in which the subscripts denote the number of the sections of the network under consideration. Thus in the sub-network 7, the value of the resistance R is Also, since R differs from R we must change the values of L or C so that and ' tively higher frequencies than the impress-ed V eet the same manner in which the magnitude of the other resistance elements is obtained.

By means of the arrangements represented in Figs. 1 and 3, having inductances in series with a source of variable voltage waves and capacities with resistances in series bridged across the said source, the integral of the impressed wave corresponding to the number of sections of network may be obtained. That is to say, with a network having four sections, the impedance of which is equal to R at all frequencies, the voltage E impressed across the input circuit of the amplifier 10 is represented by the equation "certain. critical frequency and that successive integrations tend to diminish the magnitude of the voltage values. S1nce transient inter- Ierence waves 1n submarine cables have relae signaling waves, the amplitude of the signaling voltage 1s relatively unaffected by such a network as is shown in Fig. 1, provided the frequency of the signaling wave is kept be:- low the critical frequency indicatedv by X upon the curves of Fig. 4;. It will, therefore,

be seen that thisnetwork tends to screen the receiving apparatus from the effects of a high frequency transient wave, and at the same time, to readily transmit to the said apparatus, the lower frequency signaling wave. This network, furthermore, does not require the insertion of a unilateral device between the co mponent sub-networks since there is no interaction between the various parts.

If the frequency is below a certain critical Any desired derivative ofan impressed value the'drop across C is substantially E, and the current-voltage relation is all? Equations (8) approaches Equation (10) for those low frequencies where the voltage drop across C is substantially equal to E. The output voltage, therefore, of a difierentiating net-work the derivative of the applied voltage Vifith such an arrangement of the elements, the networks, shown in Fig. 5, will be adapted to produce a voltage wave E representing the derivative of the impressed voltage wave E The relation between the voltages E and E may be represented by the equation Eg E t'r R 0 i jaw It will be seen that by grouping together any desired number of unit networks having eleof the proper values, any desired inl or erivative of" a variable voltage I be obtained. Furthermore, such network or group of networks furnish an interference reduction device which requires the use ofno unilateral device between the component unit networks to prevent interaction therebetween. This network, as has been shown, does not appreciablyaffect the magnitude of the signaling voltage waves provided the frequency thereof is kept within certain limits. Also, since the impedance of the arrangement is equivalent to pure resistance, at all frequencies, such network may be correctly terminated by a resistance element.

Although this invention has been disclosed as e'mhodiedin a particular form, it is to be understood'that it is not so limited but may be embodied in other and different forms without departing from the spirit and scope of the appended claims.

t What is claimed is 1. In a signaling system, the'combination with a transmission circuit of a terminal circuit comprising an aperiodic network made up of a group of sub-networks, each including a capacitance C in series with the circuit and a resistance R in serieswith an'inductance L bridged across the circuit, the magnitudes of the elements being such that and the sub-networks being so related that the respective capacitances are in series and the respective resistances and lnductances will be bridged in parallel across the said terminal circuit, whereby the desired derivative of any impressed wave may be obtained.

2. In a system to produce a derivative of an impressed voltage wave, the combination with a source ofa voltage wave, of an aperiodic network consisting of two branches connected in parallel across the source of the voltage wave, one of the said branches consisting ofa resistance R in series with an inductance L, and the other branch consisting of a resistance R in series with a capacity C, the said resistances being equal and the network being so proportioned that whereby a voltage which has the form of a derivative of the impressed voltage is produced in resistance R and also in inductance L, and a receiving circuit effectively connected with said aperiodic network so as to have the derivative voltage wave impressed thereon.

3. In a system to produce the derivative of an impressed voltage wave, the combination with a source of a variable voltage wave of an aperiodic network comprising a plurality of sub-networks, each including a resistance R in series with an inductance L bridged across said source, and a capacity C in series with the said source, the magnitudes of the elements being such that and the various networks being so connected that the respective capacities will be in series and the respective resistance and inductance branches will be bridged in parallel across said source, the last sub-network having a resistance R in series with the last capacity 0, whereby the voltage across the last inductance or across the resistance in series with the last capacity will be that derivative of the impressed voltage wave corresponding to the number of sub-networks employed in the said aperiodic network.

In testimony whereof, we have signed our names to this specification this 30th day of June, 1927.

' DANFORTH K. GANNETT.

MAGLEAN KIRKWOOD. 

